CHEMISTRY REVISION GUIDE for CIE IGCSE Coordinated Science ...

CHEMISTRY REVISION GUIDE for CIE IGCSE Coordinated Science (2012 Syllabus)

This revision guide is designed to help you study for the chemistry part of the IGCSE Coordinated Science course.

The guide contains everything that the syllabus says you need you need to know, and nothing extra.

The material that is in the supplementary part of the course (which can be ignored by core candidates) is highlighted in dashed boxes:

Whilst this guide is intended to help with your revision, it should not be your only revision. It is intended as a starting point but only a starting point. You should make sure that you also read your text books and use the internet to supplement your study in conjunction with your syllabus document.

Whilst this guide does contain the entire syllabus, it just has the bare minimum and is not in itself sufficient for those candidates aiming for the highest grades. If that is you, you should make sure you read around a range of sources to get a deeper knowledge and understanding.

Some very useful websites to help you further your understanding include:

? - whilst not the prettiest site this contains a lot of very useful and nicely explained information. ? e/ - well presented with many clear diagrams, animations and quizzes. Can occasionally lack depth. ? - whilst mostly targeted at A-Levels this site contains very detailed information suitable for those looking to deepen their knowledge and hit the highest grades.

Finally, remember revision is not just reading but should be an active process and could involve:

?Making notes ?Condensing class notes ?Drawing Mind-maps ?Practicing past exam questions ?Making flashcards The golden rule is that what makes you think makes you learn.

Happy studying, Mr Field.

C1: THE PARTICULATE NATURE OF MATTER

Atom: The smallest particle An atom: of matter

Some atoms:

Solids, Liquids and Gases

Molecule: A small particle Molecules of an element: Molecules of a

made from more than one

compound:

atom bonded together

Element: A substance made of only one type of atom

A solid element:

A gaseous element:

Compound: A substance A solid compound made from two or more different elements bonded together

A gaseous compound:

Mixture: A substance made from two or more elements or compounds mixed but not joined

A mixture of compounds and elements:

SOLIDS LIQUIDS AND GASES The particles in solids, liquids and gases are held near to each other by forces of attraction. The strength of these forces determines a substance's melting and boiling points.

In a solid, the forces of attraction are strongest, holding the particles tightly in position. As the solid is heated, and the particles vibrate faster, these forces are partially overcome allowing the particles to move freely as a liquid ? this is called melting. As the liquid is heated more, the particles gain so much energy that the forces of attraction break completely allowing particles to `fly around' as a gas ? this is called boiling. The reverse of the these processes are condensing and freezing. Under specific conditions, some solids can turn straight to gases ? a process called subliming (the reverse is called desubliming).

PROPERTIES Solids ?Have a fixed shape ?Can't be compressed ?Particles close together in a regular pattern ?Particles vibrate around a fixed point

Liquids ?Take the shape of their container ?Can't be compressed ?Particles close together but disordered ?Particles move freely

Gases ?Take the shape of their container ?Can be compressed ?Particles widely spaced in random order ?Particles moving very fast.

C2: EXPERIMENTAL TECHNIQUES

FILTRATION Used to separate solids from liquids. The mixture is poured through a filter paper in a funnel. The liquid can pass through the small holes in the filter paper (to become the filtrate) and the solid gets left behind (called the residue).

CRYSTALLISATION Crystallisation is used to separate mixtures of solid dissolved in liquid and relies on the fact that solids are more soluble at higher temperatures. A solution containing a solid is cooled down until crystals form in the solution, these can then be collected by filtration.

The related technique of recrystallisation can be used to separate a mixture of two soluble solids by taking advantage of the difference in their solubility. The mixture is dissolved in the smallest possible amount of hot solvent. As the solution cools, the less soluble compound forms crystals that can be collected by filtration whilst the more soluble compound stays dissolved.

DISTILLATION In distillation a mixture of liquids is separated using the differences in their boiling points. The mixture is heated until the liquid with the lowest boiling point boils, the vapours then condense on the cold surface of the condenser and the pure(er) liquid is collected.

PAPER CHROMATOGRAPHY

best possible separation of spots.

Paper chromatography is a technique that can be

used to separate mixtures of dyes or pigments and

is used to test the purity of a mixture or to see

what it contains. Firstly a very strong solution of

the mixture is prepared which is used to build up a

small intense spot on a piece of absorbent paper.

This is then placed in a jar of solvent (with a lid). As

the solvent soaks up the paper, it dissolves the

mixture-spot, causing it to move up the paper with

the solvent. However since compounds have

different levels of solubility, they move up the

paper at different speeds causing the individual

components to separate out. The solvent or

combination of solvents can be changed to get the

PURITY It is important for chemists to be able to purify the compounds they make, this is because the impurities could be dangerous or just un-useful. This is especially true for chemists making compounds that are consumed by people such as drugs or food additives since the impurities may be toxic which would be very bad news!

WHICH TECHNIQUE? You need to be able to select appropriate methods to separate a given mixture. The key to this is look for differences in the properties of the components of the mixture such as their state, solubility, melting/boiling point and so on. Then pick the method that best takes advantage of this difference.

FRACTIONAL DISTILLATION When the liquids being distilled have similar boiling points, normal distillation can't separate them completely but simply gives a purer mixture. In this case a fractionating column is used. This provides a large surface area for condensation meaning much purer `fractions' are produced. The most important use of this is separating crude oil into it's useful components.

MELTING/BOILING POINTS No two substances have the exact same melting and boiling points. We can take advantage of this to test the purity of a compound we have made. If we know what the melting or boiling point of the pure compound should be, we can then measure the melting or boiling point of a sample we have produced and the closer it is to the pure value, the more pure it is likely to be.

C3: ATOMS, ELEMENTS AND COMPOUNDS ? Structures and

Bonding

ELECTRON ARRANGEMENT/CONFIGURATION Electrons are arranged around atoms in specific shells. The most important shell is the outer one as this controls an atom's chemistry. We call the electrons in the outer shell `valence electrons' because they are used for bonding. The number of electrons in the outer shell is the same an element's group number.

The number of electrons around an atom is given by the atom's proton number. They are arranged in shells as follows:

?1st Shell ? Holds two electrons ?2nd/3rd/4th Shells ? Hold 8 electrons

?Example 1: Carbon. Proton ?Example 2: Chlorine. Proton number is 6 which means number is 17 which means there are 6 electrons: 2 in the there are 17 electrons: 2 in 1st shell and 4 in the second the 1st shell, 8 in the second

and 7 in the 3rd.

C

Cl

Checking Your Answer: To check you are right, the period gives the number of shells and the group gives the number of electrons in the outer shell. For example chlorine is in Period 3 and Group VII so it has 3 shells and 7 electrons in the outer shell.

Ions: The configuration of ions is the same as for atoms but you have to take electrons away from positive ions and add extra for negative ions. For example O/O2- Li/Li+

O

O2-

Li

Li+

Group VIII: Noble Gases Group VII: Halogens

Group II: Alkali-Earth Group I: Alkali Metals

A NOBLE MATTER

H

The Noble Gases (He, Ne, Ar

etc) have full outer shells

containing either 2 or 8

electrons. This is very stable

which is why the Noble gases

are so unreactive.

Other elements tend to react in such a way as to achieve a full outer shell by gaining or losing electrons until they achieve this Noble Gas configuration.

Transition Metals

Non-metals

Other Metals

Lanthanides and Actinides (metals)

CHEMICAL VS PHYSICAL CHANGES Physical changes are reversible whereas chemical changes are not.

For example if you melted some solid sugar to a liquid and then left it to cool, it would freeze back to solid sugar ? this is a physical change. If you took the same sugar and burned it to produce carbon dioxide and water, there would be no easy way to turn those back to sugar ? this is a chemical change ? new substances are made.

STRUCTURE OF THE PERIODIC TABLE (PT on last page!) Elements arranged in order of increasing proton number. Periods: The rows in the periodic table. ?For example Li, C and O are all in period 2. Groups: The columns in the PT. ?Use roman numbers: I, II, III, IV, V, VI, VII, VIII ?Eg. F, Cl, Br, I are all in Group VII ?Elements in the same group have similar properties and react in similar ways: the halogens all react in the same way with sodium to form sodium fluoride (NaF), sodium chloride (NaCl), sodium bromide (NaBr) and sodium iodide (NaI)

ISOTOPES Isotopes are atoms with the same proton number but different nucleon number.

For example carbon has two main isotopes ? C-12 and C-13. Carbon has a proton number of 6 so they both contain 6 protons and 6 electrons but C-12 has 6 neutrons and C13 has 7.

ATOMIC STRUCTURE

what the element is.

Atoms are made of: Protons: mass = 1, charge = +1 Neutrons: mass = 1, charge = 0 Electrons: mass = 0, charge = -1

In a square on the periodic table the smaller number, the proton number, gives the number of protons or electrons and the

The numbers of each vary from bigger number, the nucleon

element to element but it is the number the number of protons

number of protons which decides and neutrons together.

Eg 1: Boron has 5 protons, 6 neutrons (ie 11-5) and 5 electrons

Eg 2: Phosphorus has 15 protons, 16 neutrons (ie 31-16) and 15 electrons

Group VIII: Noble Gases Group VII: Halogens

C3: ATOMS, ELEMENTS AND COMPOUNDS ? Bonding and

Structure

MOLECULES A molecule is a small particle made from (usually) a few non-metal atoms bonded together.

The atoms in a molecule are joined by strong covalent bonds. In a solid each molecule is held close to its neighbour by weak intermolecular forces.

When a substance melts, it is these weak intermolecular forces that break NOT the strong covalent bonds.

Molecular compounds have low melting points and are volatile (evaporate easily) due to the weak intermolecular forces, and insulate electricity as all electrons are stuck in bonds and so unable to move.

IONIC BONDING

Awnheionnaictobmonsd(uissuthalelyamtteratactlsio) lnobseetewleecetrnotnws.oAonpiopnossi(tneelygacthivaerg)eadreiofonrsm. Ceadtiwonhsen(paoNtsooitmniv-sem()uaesrtueaalflsloyrnmoend-

metals) gain electrons.

Atoms will lose or gain electrons until they have a complete outer shell: elements in Groups I, II and III will lose 1, 2 and 3 electrons respectively to form 1+, 2+ and 3+ ions. Atoms in Groups V, VI and VII gain 3, 2 and 1 electrons to form 3-, 2- and 1- ions. In an ionic compound the number of positive and negative and charges must cancel out to neutral.

Example: NaF, sodium in Group I forms a 1+ ion Example: Li2O, lithium in Group I forms a 1+ ion and fluorine in group VII forms a 1- ion so one but oxygen in Group VI forms a 2- ion so two Li+

Na+ is needed to balance out one F-

are needed to balance out one O2-

F-

Na+

Li+

O2-

Li+

GIANT COVALENT LATTICES Graphite: made of carbon

A crystal made of a repeating atoms arranged in hexagonal

pattern of atoms joined with sheets with long weak bonds

covalent bonds that repeats between the sheets. This

millions of times in all

means the sheets can easily

directions.

separate making graphite a

good lubricant:

Diamond is made of carbon

atoms arranged so that each C

is bonded in a pyramid

arrangement to 4 others. This

makes it very hard, ideal for use

in industrial drills:

Silicon (IV) oxide (SiO2) has a structure with each Si

joined to 4 O and each O

joined to 2 Si. It is

the main ingredient

in glass.

COVALENT BONDING A covalent bond forms between two atoms and is the attraction of two atoms to a shared pair of electrons. Small groups of covalent bonded atoms can join together to form molecules.

The atoms share enough electrons to complete their outer

sEhxeallms.ple: H2O*, hydrogen is Example: CO2*, carbon is has has one valence electron and four valence electrons so

needs one more to complete needs four more to complete

the 1st shell, oxygen has six its outer shell, oxygen needs

valence electrons electrons so two more. Thus each carbon

needs two more. Thus one will react with two oxygens,

oxygen will react with two sharing two electrons with

hydrogens:

each one. A bond involving

two shared pairs is a double

bond.

H

O

H

O

C

O

*Nb: In these diagrams only draw the outer shell and use different shapes/colours to show where electrons have come from. You should be able to draw at least: H2O, CH4, Cl2, HCl, H2, N2, O2, CO2, C2H4

GIANT IONIC LATTICES The positive and negative ions in an ionic compound don't form molecules but form crystals made of a repeating pattern of positive and negative ions called a giant ionic lattice. Eg sodium chloride:

Properties of Ionic Compounds When you melt or dissolve an ionic compound it conducts electricity because the ions are free to move towards the positive and negative electrodes. When solid the ions are stuck in position and there are no free electrons so they don't conduct.

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